Iron oxides of reduced chloride content

ABSTRACT

A process for removing chloride from chloridic iron oxide comprises mixing said chloridic iron oxide with an acid and subsequently conducting a thermal treatment at from 50 to 1300° C.

[0001] The present invention relates to a process for removing chloridefrom chloridic iron oxide, which comprises mixing said chloridic ironoxide with an acid and subsequently subjecting the mixture to a thermaltreatment at elevated temperatures.

[0002] Iron oxides containing residual chloride are generated in someindustrial processes. An important example is the work-up ofhydrochloric acid waste liquids generated from steel pickling whereinthe hydrochloric acid pickling waste, which contains iron chloride, issprayed into a roaster where it is reacted with oxygen to form mainlyFe₂O₃ (hematite) and hydrogen chloride. This process generally leaves anappreciable fraction of residual chloride in the iron oxide. Theresidual chloride content of such iron oxides is typically in the rangefrom 800 to 3000 ppm. The chloride content of iron oxides of this typeleaves something to be desired for industrial applications.

[0003] WO-A-96/32355 discloses a process for reducing the chloridecontent of such iron oxides by mixing the chloride-containing iron oxidewith a hydrated metal compound and water and a subsequent calcination.The use of a hydrated metal compound makes the process costly andinconvenient.

[0004] It is an object of the present invention to remedy thisdisadvantage.

[0005] We have found that this object is achieved by a novel andimproved process for removing chloride from chloridic iron oxide, whichcomprises mixing said chloridic iron oxide with an acid and subsequentlyconducting a thermal treatment at from 50 to 1300° C.

[0006] The process of the invention can be carried out as follows:

[0007] The chloridic iron oxide may be mixed with an acid and thensubjected to a thermal treatment at from 100 to 1300° C.

[0008] Useful chloridic iron oxides include in particular those whichare produced by spray roasting hydrochloric acid pickling wastes in thesteel industry and are present as Fe₂O₃ (hematite) having a residualchloride content in the range from 800 to 20,000 ppm, referably in therange from 800 to 5000 ppm, particularly referably in the range from 800to 2000 ppm. The iron oxide used may also include other impurities. Suchimpurities, which are frequently present in technical grade iron oxides,include for example compounds of titanium, manganese, aluminum,chromium, phosphorus, zinc, copper, molybdenum, silicon, nickel,magnesium, potassium, sodium, cobalt, niobium, sulfur and/or calcium.

[0009] Useful acids include organic acids and inorganic acids, in pureor dilute form, except acids that contain C1 in the acid molecule.Useful acids include for example carboxylic acids, preferably C₁- toC₂₀-carboxylic acids, particularly preferably C₁- to C₈-alkylcarboxylicacids, especially C₁- to C₄-alkylcarboxylic acid such as formic acid andacetic acid, preferably inorganic acids such as mineral acids, exceptacids that contain C1 in the acid molecule, for example nitric acid,nitrous acid, phosphoric acid, phosphorous acid, sulfuric acid orsulfurous acid, preferably dilute (aqueous) 0.1-50% by weight,preferably 0.2-25% by weight, particularly preferably 0.5-15% by weightacids, particularly preferably dilute acids which are decomposable orcompletely removable in the course of the thermal treatment. Veryparticular preference is given to using dilute 0.5-50% by weight,preferably 0.5-25% by weight, particularly preferably 0.5-15% by weight,nitric acid.

[0010] The iron oxide may be mixed with the acid to form a liquidsuspension, preferably a moist mass, in which case typically allcustomary mixing means, preferably mixers, kneaders or mullers are used.To prepare a moist mass of iron oxide and an acid, it is typical to usefrom 10 to 3000 ml, preferably from 50 to 2000 ml, particularlypreferably from 100 to 1500 ml, especially from 400 to 1200 ml, of anoptionally aqueous dilute acid per kilogram of iron oxide. The mixingmay be carried out discontinuously, batchwise, semicontinuously orcontinuously.

[0011] After mixing, the mixture may be left to stand for some time orbe thermally treated directly. To thermally treat the mixture, it may betreated discontinuously, batchwise, semicontinuously or continuously ata single temperature or at different temperatures. The thermal treatmentmay generally be carried out at from 50 to 1300° C. The thermaltreatment generally comprises,a drying step at from 50 to 300° C.,preferably from 80 to 200° C., particularly preferably from 90 to 180°C., and a calcining step at from 450 to 1300° C., preferably from 550 to1200° C., particularly preferably from 600 to 1100° C. A particularlypreferred embodiment comprises a calcining step at from 650 to 750° C.and a subsequent calcining step at from 850 to 1000° C. It is alsopossible to calcine directly at from 850 to 1000° C. without priorcalcination at from 650 to 750° C.

[0012] The reduced residual chloride content iron oxide treatedaccording to the invention generally has a residual chloride content offrom 10 to 800 ppm, preferably from 15 to 700 ppm, particularlypreferably from 20 to 250 ppm, especially from 25 to 150 ppm, andgenerally has a, hematite structure and is useful for a whole series ofindustrial applications such as pharmaceuticals, cosmetics, magnetictape coatings, chemical reactions, catalysts, especially to producecatalysts for dehydrogenating ethylbenzene to styrene.

EXAMPLES

[0013] All examples were carried out using the HP (Hösch Premium) ironoxide from Thyssen-Krupp. The residual chloride content was in all casesdetermined coulometrically. The untreated HP iron oxide had a residualchloride content of 1400 ppm. All values are compared in Table 1.

Example 1

[0014] 200 g of the iron oxide were mixed with 125 ml of 1% HNO₃. Themixture was then left to stand at room temperature for one hour, driedat 120° C. for 16 h and calcined at 700° C. for 1 h.

Example 2

[0015] Example 1 was repeated using 125 ml of 5% HNO₃.

Example 3

[0016] Example 1 was repeated using 125 ml of 10% HNO₃.

Example 4

[0017] Example 1 was repeated except that the mixture from thecalcination at 700° C. was further calcined at 900° C. for one hour.

Example 5

[0018] Example 4 was repeated using 125 ml of 5% HNO₃.

Example 6

[0019] Example 4 was repeated using 125 ml of 10% HNO₃. TABLE 1 Chloridecontent of untreated iron oxide and of iron oxides treated according tothe invention. Residual chloride Iron oxide [ppm] Untreated HP(Thyssen-Krupp) 1400 Example 1 (1% HNO₃/700° C.) 680 Example 2 (5%HNO₃/700° C.) 610 Example 3 (10% HNO₃/700° C.) 570 Example 4 (1%HNO₃/900° C.) 86 Example 5 (5% HNO₃/900° C.) 60 Example 6 (10% HNO₃/900°C.) 64

We claim:
 1. A process for removing chloride from chloridic iron oxide,which comprises mixing said chloridic iron oxide with an acid andsubsequently conducting a thermal treatment at from 50 to 1300° C.
 2. Aprocess as claimed in claim 1, wherein said thermal treatment comprisesa drying step at from 50 to 300° C. and a calcining step at from 450 to1300° C.
 3. A process as claimed in claim 1, wherein said thermaltreatment comprises a calcining step at from 650 to 750° C. andsubsequently a calcining step at from 850 to 1000° C.
 4. A process asclaimed in claim 1, wherein said acid used is an organic or inorganicacid selected from acids that do not contain C1 in the acid molecule. 5.A process as claimed in claim 1, wherein said acid is dilute, aqueousand from 0.1 to 50% by weight in strength.
 6. A process as claimed inclaim 1, wherein said acid is dilute, aqueous 0.5-15% by weight nitricacid.
 7. A process as claimed in claim 1, wherein said chloridic ironoxide is produced by spray roasting hydrochloric acid waste liquidsgenerated from steel pickling.
 8. Iron oxide prepared as claimed inclaim 1, characterized by a residual chloride content of from 10 to 800ppm.
 9. The use of iron oxide as claimed in claim 1 for pharmaceuticals,cosmetics, magnetic tape coatings, chemical reactions, catalysts,especially to produce catalysts for dehydrogenating ethylbenzene tostyrene.